This project is concerned with the structures, biosynthesis and function of the polymethylpolysaccharides in Mycobacterium smegmatis. The polymethylpolysaccharides consist of the 6-0-methylglucose-containing lipopolysaccharides (MGLP) and the 3-0-methylmannose polysaccharides (MMP). Both are unique in that they are the only known naturally-occurring polysaccharides with long sequences of methylated sugars. Moreover, they have been shown to have the unusual function in the cell of regulating fatty acid synthesis through a mechanism that involves interaction with the enzyme complex and with the acyl-CoA products. The very limited occurrence of these substances and their important role in these bacteria suggest that structural analogs might be designed that are good inhibitors of fatty acid synthesis. If so, they could have important clinical application in treatment of tuberculosis and leprosy. Although we have already determined many of the structural features of these substances, both MGLP and MMP exist in numerous isomeric forms, and our present program is aimed at defining the differences between these isomers. In terms of their biosynthesis, the most interesting question concerns how the methylating enzymes recognize the acceptors and terminate methylation at the proper stage. Finally, our interest in the mechanism of function deals with the precise manner in which the polysaccharides interact with the different acyl-CoA products. We are planning to design very sensitive probes so that these interactions can be studied below the critical micellar concentrations of the lipids in the hope that such studies will yield useful information.